Pollution control devices are employed on motor vehicles to control atmospheric pollution. Such devices include catalytic converters and diesel particulate filters. Catalytic converters typically contain a ceramic monolithic structure which supports the catalyst. The monolithic structure may also be made of metal. Diesel particulate filters or traps are wall flow filters which have honeycombed monolithic structures typically made from porous crystalline ceramic materials.
Each of these devices has a metal housing (typically stainless steel) which holds a ceramic or steel monolithic structure. The ceramic monolithic structures generally have very thin walls to provide a large surface area for the catalyst and are fragile and susceptible to vibration damage and breakage. The ceramic monolithic structures or monoliths have a coefficient of thermal expansion generally an order of magnitude less than the metal housing which contains them. To avoid damage to the ceramic monoliths from road shock and vibrations, to compensate for the thermal expansion difference, and to prevent exhaust gases from passing between the monoliths and the metal housings, ceramic mats or paste materials are disposed between the ceramic monoliths and the metal housings. The process of placing or disposing of the mounting material or mat is also called canning and includes such processes as injecting a paste into a gap between the monolith and the metal housing, or wrapping a sheet or mat material around the monolith and inserting the wrapped monolith into the housing.
Typically, the paste or sheet mounting materials include inorganic binders, inorganic fibers, intumescent materials, organic binders, fillers and other adjuvants. The materials may be used as sheets, mats, or pastes. Known mat materials, pastes, and intumescent sheet materials used for mounting a monolith in a housing are described in, for example, U.S. Pat. Nos. 3,916,057 (Hatch et al.), 4,305,992 (Langer et al.), 4,385,135 (Langer et al.), 5,254,410 (Langer et al.), 5,242,871 (Hashimoto et al.), 3,001,571 (Hatch), 5,385,873 (MacNeil), 5,207,989 (MacNeil), and GB 1,522,646 (Wood).